(i) Field of the Invention
The present invention relates to a nylon composition having increased hydrolyzability and a method for increasing the hydrolyzability of a nylon.
(ii) Description of the Prior Art
Nylons are produced in large quantities on an industrial scale and utilized in many occasions of daily lives, because of being excellent in wear resistance, toughness, chemical resistance, heat resistance, cold resistance and moldability.
As widely known, however, it is difficult to decompose the nylons under natural circumstances. Therefore, when various kinds of materials and molded articles made from nylons become unnecessary and are disposed without burning them, they are stored as waste for a long period of time. The amount of the waste remarkably increases with the development of industry, which is a serious social problem nowadays in the world.
If the hydrolyzability of the nylons can be increased, this will be a means effective to solve the above-mentioned problem. That is, if the various kinds of materials and molded articles made from nylon are disposed of after the period of use, and their weight, volume, strength and the like are then decreased or deteriorated by rapid hydrolysis. This will largely contribute to the protection of the environment.
Nevertheless, there have been found neither a nylon composition which can be effectively hydrolyzed under the natural circumstances nor a method for imparting, to the nylons, characteristics by which they can be effectively hydrolyzed under natural circumstances.
For example, Japanese Patent National Publication (Kohyo) No. 500076/1988 (PCT/US 86/01168; the fundamental application of the priority in U.S. Ser. No. 754870, now U.S. Pat. No. 5,013,315) discloses a bone plate spacer made from a resin composition containing an unabsorbable polymer and an absorbable polymer.
As the unabsorbable polymer which can be preferably used in the bone plate spacer, polyurethanes, polyalkylenes and nylons are disclosed, and as the absorbable polymer, polyesteramides, polyglycolic acid, polylactic acid, polydioxanone, polytrimethylene carbonate and the like are disclosed.
However, this patent publication separately discloses the nylon which is an unabsorbable polymer as well as the polyglycolic acid, the polylactic acid, a glycolic acid copolymer and a lactic acid copolymer which are the absorbable polymers, and it does not reveal any embodiments regarding pairs of the nylon and the polyglycolic acid, the nylon and the polylactic acid, the nylon and the glycolic acid copolymer, and the nylon and the lactic acid copolymer.
Accordingly, the unabsorbable polymer constituting the bone plate spacer disclosed in the patent publication still tenaciously remains undecomposed in an elastic state, after the absorbable polymer has been absorbed.
As is apparent from the foregoing, there have been known neither the nylon composition which can be effectively hydrolyzed under natural circumstances nor the method for imparting, to the nylon, characteristics by which they can be effectively hydrolyzed under the natural circumstances.